Seasonal variation in element concentrations in surface sediments of three rivers with different pollution input in Serbia

Abstract

Purpose: The main objective of this study was to evaluate the concentrations and seasonal variations of trace elements in surface sediments of three major rivers in Serbia—the Danube, the Zapadna Morava (ZM), and the Južna Morava (JM)—according to sediment quality guidelines. The ZM and the JM create the Velika Morava River, one of the most important tributaries of the Danube, which has been characterized as a source of heavy metal pollution. Materials and methods: The total concentrations of 15 elements (Al, As, B, Ba, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sr, and Zn) were determined in surface sediments (0–15 cm depth) collected during three seasons using inductively coupled plasma spectroscopy (ICP-OES). Principle component analysis (PCA) was used to identify the main variations in metal concentrations and grain size distribution. Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS) was used for grain analysis. Results and discussion: PCA and three-way MANOVA results showed significant differences in element concentrations and grain size distribution between the rivers, and significant seasonal differences for each river. The concentrations of Cu and Ni exceeded sediment quality guideline levels in the ZM and the Danube, respectively, while excess Hg was detected in all three rivers. Concentrations of Al, Ba, Cu, Fe, Sr, and Zn significantly varied between seasons in the Danube and the ZM, being the highest in the summer. In the JM, concentrations of Al, As, Fe, Mn, and Zn varied with season, with the lowest values in the summer. The ZM had the highest percentage of silt and clay, and SEM-EDS analysis of ZM sediments showed associations of Cu with carbonate hydroxides and/or iron oxides in particles <100 μm. The results suggested that mining and industrial activities could be the sources of increased levels of metals in the ZM. Conclusions: The sediments collected from the ZM were considerably more polluted with heavy metals in comparison to the JM. Cu was identified as a heavy metal of greatest risk in the ZM. The ZM was indicated as the main source of heavy metal delivery in the Velika Morava and Danube rivers. It is suggested that the main factors influencing pollution levels could be anthropogenic sources and industrial and mining activities, while seasonal changes might be related to dynamics of water flow and morphological characteristics of the two tributary rivers.